Polyelectrolyte Block Research Articles

Wormlike core–shell nanoparticles formed by co-assembly of double hydrophilic block polyelectrolyte with oppositely charged fluorosurfactant

Formation of polyelectrolyte–surfactant complexes (PE–S) between an anionic polyelectrolyte, poly(sodium 2-sulfamate-3-carboxylate isoprene)-block-poly(ethylene oxide) (PSCI-PEO) and a cationic fluorosurfactant, N-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl) pyridinium chloride (HFDPCl) was studied in alkaline aqueous solutions by static, dynamic and electrophoretic light scattering. The structure of the formed PE–S nanoparticles was investigated by SAXS, cryogenic transmission electron microscopy and atomic force microscopy. The results show that the tendency of the fluorosurfactant to form elongated threadlike micelles drives the PE–S co-assembly to a flexible core–shell cylindrical morphology with the core of the PE–S and the shell of the PEO blocks. Unlike other PE–S systems involving double hydrophilic polyelectrolytes, well-defined core–shell particles exist only in the narrow range of HFDPCl-to-PSCI unit stoichiometric ratios corresponding to zero ζ-potential of the aggregates.

Salt Effects on Sol–Gel Transition of Telechelic Polyelectrolytes in Aqueous Solutions

Using Monte Carlo simulation techniques, we focus on the physical gelation behavior and conformation change under the existence of additional monovalent salt, which provides screening to the electrostatic interaction of charged telechelic polyelectrolyte chains and causes new balance between hydrophobic interaction of end groups and electrostatic interaction originated from the polyelectrolyte blocks. For the electrostatic interaction dominated system, the screening effects will decrease the electrostatic repulsion between small sized clusters and enable the further aggregation of TP chains, resulting in prompting the sol–gel transition progress; for the short-range attraction dominated system, the screening effects present a complicated phenomenon, which includes the prompting effect at the beginning of sol–gel transition and a hindering effect when the gelation progress is close to an end.

Hierarchical Organometallic Materials: Self-Assembly of Organic–Organometallic Polyferrocenylsilane Block Polyelectrolyte–Surfactant Complexes in Bulk and in Thin Films

The self-assembly of well-defined organic–organometallic polystyrene-b-poly(ferrocenylmethyl(dimethylaminopropynylsilane)) (PS-b-PFAMS) diblock copolymers has been systematically investigated by varying the volume fraction of the organometallic block (PFAMS). Quaternization of the PFAMS block yielded PS-b-qPFAMS, which was ionically complexed to the anionic surfactants sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and sodium bis(2,2,3,3,4,4,5,5,5-nonafluoropentyl) sulfosuccinate (AOTF). The self-assembly of the block copolymer-surfactant complexes was also studied in bulk and thin films and produced materials with structural hierarchy over multiple length scales as shown by AFM, TEM, and SAXS studies.

Conformations of Amphiphilic Polyelectrolyte Stars with Diblock Copolymer Arms

We consider conformations and intra-molecular conformational transitions in amphiphilic starlike polymers formed by diblock copolymer arms with inner hydrophobic and outer polyelectrolyte blocks. A combination of an analytical mean-field theory with the assumption-free numerical self-consistent field (SCF) modeling approach is applied. It is demonstrated that unimolecular micelles with collapsed hydrophobic cores and swollen polyelectrolyte coronae are formed in dilute aqueous solutions at high ionic strength or/and low degree of ionization of the outer hydrophilic block. An intra-molecular conformational transition related to the unfolding of the hydrophobic core of the unimolecular micelles can be triggered by a decrease in the ionic strength of the solution or/and increase in the degree of ionization of the coronal blocks. In the stars with large number of diblock copolymer arms the transition between conformations with collapsed or stretched core-forming blocks occurs continuously by progressive unfolding of the core domain. By contrast, in the stars with relatively small number of arms the continuous unfolding of the core is interrupted by an abrupt unravelling transition. A detailed SCF analysis indicates that under both unfolding scenario the arms of the star are extended fairly equally, i.e., no intra-molecular disproportionation occurs.

Block copolymer micelles with a mixed amphiphilic corona composed of polyelectrolyte and uncharged blocks

Block copolymer micelles with a mixed amphiphilic corona composed of polyelectrolyte and uncharged blocks

Rheology and SANS on PET-b-PLAc-b-P(DMAEMAq) Triblock Copolymers: Impact of the PET and Polyelectrolyte Chain Length

We report on a small angle neutron scattering (SANS) study of self-organization of a novel triblock copolymer containing a crystalline poly(ethylene terephthalate) oligomer, a rubbery poly(lauryl acrylate) midblock, and a polyelectrolyte block (quaternized poly(2-(dimethylamino)ethyl methacrylate)) of various length. The rheology of the solutions showed a transition from Newtonian flow at low concentrations, to shear-thinning at intermediate concentrations, and finally a yield behavior at high concentrations. The microstructure of the samples investigated by SANS was found to evolve strongly with the polyelectrolyte block length. The data were analyzed in terms of aggregation numbers, radius of gyration, and aggregate hydration. Complete modeling of the intensity curves was achieved by an inversion method extracting an average aggregate radial volume fraction profile. In both rheology and microstructure, a surprising strong impact of the small PET block was observed.

The Effect of UV Irradiation on the Transmittance Bands of Polystyrene-block-2-vinylpyrimidine

Block copolymers have been investigated for fabricating functional nanomaterials due to their properties of self-assembly. We prepared polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) lamellar films which is hydrophobic block-hydrophilic polyelectrolyte block polymer have 57 kg/mol-b-57 kg/mol. The lamellar stacks are obtained by exposing the spin coated film under chloroform. The P2VP blocks were then quaternized and crosslinked to various extents using 5 wt% of iodomethane. PS-b-P2VP films showed excellent photonic bands at 630 nm after swelling with ethanol and 661 nm with water after treated with Calcium Carbonate. We observed significant band shift from 663 nm (deep red) to 531 nm (green) during UV-irradiation for 40 seconds. The phase separation process of BCP was very sensitive to the film thickness. The quarternized films with thickness varied from 0.43 µm (446 nm transmittance minimum) to 0.25 μm (478 nm transmittance minimum). This study shows that the total film thickness and UV irradiation effectively change the transmittance band by affecting the thickness of layers consisting of PS-b-P2VP photonic crystals.

The Color Tuning of PS-b-P2VP Lamellar Films with Changing the Alkyl Chain Length of 1-Iodoalkanes

Photonic crystals with tunability in the visible or near-infrared region have drawn increasing attention for controlling and processing light for the active components of future display. We prepared polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) lamellar films which is hydrophobic block-hydrophilic polyelectrolyte block polymer of 57 kg/mol-b-57 kg/mol. The lamellar stacks, which is alternating layer of hydrophilic and hydrophobic moiety of PS-b-P2VP, are obtained by exposing the spin coated film under chloroform vapor. The band gaps of the lamellar films interestingly varied after immersion into the quaternizing solvents containing 5 wt% of iodomethane, iodoethane, 1-iodobutane, 1-iodopentane, 1-iodohexane and 1-iodooctane solubilized in n-hexane. The iodoalkanes reacted with pyridine groups in PS-b-P2VP and generated the alkyl pyridinium salts readily. The degree of quaternization, alkyl chain length of iodoalkane and the salt water concentration affects the spacing of layer structure of PS-b-P2VP. The iodomethane and iodohexane produced similar band gaps and salt concentration dependence. These results are very much dependent on the hydrophobic-hydrophilic characters of PS-b-P2VP lamellar surface.

CdS-containing nano-assemblies of double hydrophilic block copolymers in water

Two samples of poly(sodium(sulfamate-carboxylate)isoprene)-block-poly(ethylene oxide) copolymer (SCIEO-1 and SCIEO-2) differing in molecular weight and relative length of polyelectrolyte blocks have been used as templates for the synthesis of cadmium sulfide (CdS) nanoparticles in aqueous media. The double-hydrophilic copolymer SCIEO has very high 1D charge density, and its polymer chain structure mimics that of polysaccharide heparin. It is soluble in aqueous media, but the addition of cadmium acetate (Cd(Ac)2) to its aqueous solution causes the formation of micellar aggregates with Cd2+containing insoluble cores above the threshold Cd2+ concentration. The trapped Cd2+ ions can be chemically transformed to CdS nanoparticles. The stability of hybrid SCIEO/CdS micelles depends on the ratio of PEO-to-SCI lengths: it was found that the SCIEO-2 copolymer with sufficiently long PEO block behaves as an effective stabilizer for the synthesis of CdS nanoparticles embedded in micelles, while SCIEO-1 does not. The morphology of aggregates varies with the Cd-to-SCI ratios and ranges from spherical to mixture of spherical and necklace-like micellar aggregates. A number of experimental techniques including static and dynamic light scattering, fluorescence correlation spectroscopy, atomic force and transmission electron microscopy, UV-vis, and fluorescence spectroscopy were employed for the characterization of both CdS containing hybrid micelles and embedded CdS nanoparticles.

Novel sulfonated block copolymer containing pendant alkylsulfonic acids: Syntheses, unique morphologies, and applications in proton exchange membrane

In this article, we report the syntheses and characterizations of a series of novel block polyelectrolytes, poly(styrene-block-sulfonated hydroxystyrene) (PS-b-sPHS), containing pendant sulfonic acid groups attached to the backbone via propyl spacers in the sPHS domain. PS-b-sPHS with various compositions were synthesized via anionic polymerization and the following analogous chemistry to achieve accurate control of molecular weight (Mw), narrow polydispersity and high degree of sulfonation. Proton exchange membranes (PEMs) were prepared from PS-b-sPHS with sulfonic acids in either potassium salts or tetra-alkylammonium salts via solvent casting and following treatments. Some unique morphologies, such as hallow channels and lamellar arrangement of strings of beads, were observed as a consequence of equilibrium between microphase separation and columbic interactions between polyelectrolytes. The transportation properties were found to closely relate to the morphologies of the PEMs. The combination of microphase separation of block polyelectrolytes and freedom of movement of pendent alkylsulfonic acids was demonstrated to effectively enhance the proton transport and suppress the methanol crossover for the PEMs, leading to the selectivity higher than Nafion 117 by five times at most. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Polyelectrolyte−Surfactant Complexes Formed by Poly[3,5-bis(trimethylammoniummethyl)4-hydroxystyrene iodide]-block-poly(ethylene oxide) and Sodium Dodecyl Sulfate in Aqueous Solutions

Formation of polyelectrolyte-surfactant (PE-S) complexes of poly[3,5-bis(trimethylammoniummethyl)-4-hydroxystyrene iodide]-block-poly(ethylene oxide) (QNPHOS-PEO) and sodium dodecyl sulfate (SDS) in aqueous solution was studied by dynamic and electrophoretic light scattering, small-angle X-ray scattering (SAXS), atomic force microscopy, and fluorometry, using pyrene as a fluorescent probe. SAXS data from the QNPHOS-PEO/SDS solutions were fitted assuming contributions from free copolymer, PE-S aggregates described by a mass fractal model, and densely packed surfactant micelles inside the aggregates. It was found that, unlike other systems of a double hydrophilic block polyelectrolyte and an oppositely charged surfactant, PE-S aggregates of the QNPHOS-PEO/SDS system do not form core-shell particles and the PE-S complex precipitates before reaching the charge equivalence between dodecyl sulfate anions and QNPHOS polycationic blocks, most likely because of conformational rigidity of the QNPHOS blocks, which prevents the system from the corresponding rearrangement.

Synthesis and pH/Temperature‐Responsive Behavior of PLLA‐b‐PDMAEMA Block Polyelectrolytes Prepared via ROP and ATRP

AbstractWell‐defined diblock poly(L‐lactide)‐block‐poly(dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were synthesized by combining ROP of LLA and ATRP of DMAEMA, from a dual‐initiator 2‐hydroxylethyl 2‐bromoisobutyrate. The molecular characterization of these diblock copolymers was performed using 1H NMR, FT‐IR, and GPC‐MALLS analysis. The responsive behavior of these diblock copolymers in aqueous solutions at different pH and temperatures were investigated using DLS. Results show that both higher pH and temperature result in a higher degree of neutralization, weaker hydrogen bonding, and micellar aggregation. As observed by TEM, changes in micellar morphology are in accordance with DLS results. magnified image

Micellization of copolymers via noncovalent interaction with TPPS and aggregation of TPPS

Aggregation of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (TPPS) was investigated in complex micelles composed of poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP) and poly(2-(dimethylamino)ethyl methylacrylate)-b-poly(N-isopropylacrylamide) (PDMAEMA-b-PNIPAM) in aqueous solutions. The resultant complex micelles had a complex P4VP/PDMAEMA/TPPS core and a mixed PEG/PNIPAM shell. Different noncovalent interaction modes between the porphyrin and each copolymer accomplished a co-effect on the aggregation of TPPS. The formation of aggregates was pH-dependent. At pH 3.2–6.5, TPPS existed as a mixture of H-aggregates and monomers because of the aromatic-aromatic interaction with P4VP and electrostatic interaction with PDMAEMA. The monomers translated into J-aggregates, stabilized by electrostatic interaction with the both polyelectrolyte blocks, upon decreasing the pH to 1.6. The free-base monomer was the one and only form for the dye at pH 11.0 due to aromatic stacking with the pyridyl rings.

Self-assembly in block polyelectrolytes

The self-consistent field theory (SCFT) complemented with the Poisson-Boltzmann equation is employed to explore self-assembly of polyelectrolyte copolymers composed of charged blocks A and neutral blocks B. We have extended SCFT to dissociating triblock copolymers and demonstrated our approach on three characteristic examples: (1) diblock copolymer (AB) melt, (2) symmetric triblock copolymer (ABA) melt, (3) triblock copolymer (ABA) solution with added electrolyte. For copolymer melts, we varied the composition (that is, the total fraction of A-segments in the system) and the charge density on A blocks and calculated the phase diagram that contains ordered mesophases of lamellar, gyroid, hexagonal, and bcc symmetries, as well as the uniform disordered phase. The phase diagram of charged block copolymer melts in the charge density--system composition coordinates is similar to the classical phase diagram of neutral block copolymer melts, where the composition and the Flory mismatch interaction parameter χ(AB) are used as variables. We found that the transitions between the polyelectrolyte mesophases with the increase of charge density occur in the same sequence, from lamellar to gyroid to hexagonal to bcc to disordered morphologies, as the mesophase transitions for neutral diblocks with the decrease of χ(AB). In a certain range of compositions, the phase diagram for charged triblock copolymers exhibits unexpected features, allowing for transitions from hexagonal to gyroid to lamellar mesophases as the charge density increases. Triblock polyelectrolyte solutions were studied by varying the charge density and solvent concentration at a fixed copolymer composition. Transitions from lamellar to gyroid and gyroid to hexagonal morphologies were observed at lower polymer concentrations than the respective transitions in the similar neutral copolymer, indicating a substantial influence of the charge density on phase behavior.

Fluorescence enhancement by microphase separation-induced chain extension of Eu3+ coordination polymers: phenomenon and analysis

In this paper, we report on the fluorescence enhancement of Eu coordination complexes in dilute solutions through electrostatic complex micelle formation with an oppositely charged block polyelectrolyte. The coordination complexes alone are oligomeric structures which have many ends where partially coordinated europium is exposed to water. In the presence of oppositely charged polyelectrolytes, the local concentration of the coordination complexes is greatly enhanced, so that they transform into polymeric structures and form electrostatically induced micelles with the block polyelectrolytes. This effectively decreases the number of europium–water coordination bonds, which leads to the enhancement of fluorescence emission. This is the first report that utilizes the concentration responsiveness of the smart coordination polymers to promote the function of the colloids made from them.

Self-association behavior in water of an amphiphilic diblock copolymer comprised of anionic and dendritic blocks

Well-defined amphiphilic diblock copolymers (PAMPS-b-PG2) composed of a hydrophilic linear polyelectrolyte and hydrophobic blocks bearing pendent dendritic moieties was synthesized via reversible addition–fragmentation chain transfer (RAFT) controlled radical polymerization of 3,5-bis[3′,5′-bis(benzyloxy)benzyloxy]benzyl 11-acrylamidoundecanoate (G2) using a poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) (PAMPS) based macro-chain transfer agent. Degrees of polymerization of PAMPS and PG2 blocks were 71 and 3, respectively. The polydispersity index was 1.25 as estimated from GPC. Hydrophobic association of the PG2 blocks in aqueous solutions was suggested from restricted motions of the dendritic moieties as observed by 1H NMR in D2O. A fluorescence spectrum of 8-anilino-1-naphthalenesulfonic acid, ammonium salt hydrate indicated that the fluorescence probe was solubilized in the hydrophobic domain formed from the polymer aggregate in water. The formation of polymer aggregates was indicated by light scattering data. The hydrodynamic radius (Rh) of the polymer aggregate was independent of the polymer concentration.

Polyelectrolyte Complex Optimization for Macrophage Delivery of Redox Enzyme Nanoparticles

We posit that cell-mediated drug delivery can improve transport of therapeutic enzymes to the brain and decrease inflammation and neurodegeneration seen during Parkinson's disease. Our prior works demonstrated that macrophages loaded with nanoformulated catalase ('nanozyme') then parenterally injected protect the nigrostriatum in a murine model of Parkinson's disease. Packaging of catalase into block ionomer complex with a synthetic polyelectrolyte block copolymer precludes enzyme degradation in macrophages. We examined relationships between the composition and structure of block ionomer complexes with a range of block copolymers, their physicochemical characteristics, and loading, release and catalase enzymatic activity in bone marrow-derived macrophages. Formation of block ionomer complexes resulted in improved aggregation stability. Block ionomer complexes with ε-polylysine and poly(L-glutamic acid)-poly(ethylene glycol) demonstrated the least cytotoxicity and high loading and release rates. However, these formulations did not efficiently protect catalase inside macrophages. Nanozymes with polyethyleneimine- and poly(L-lysine)(10)-poly(ethylene glycol) provided the best protection of enzymatic activity for cell-mediated drug delivery.

Direct and Inverse Micelles of Diblock Copolymers with a Polyelectrolyte Block: Effect of Equilibrium Distribution of Counterions

We develop a mean-field theory of micelle formation in salt-free solution of diblock copolymers with a soluble polyelectrolyte block and an insoluble neutral block. The so-called three-zone model i...

On the stability of the polymer brushes formed by adsorption of Ionomer Complexes on hydrophilic and hydrophobic surfaces

We have studied the effect of normal forces and shear forces on the stability and functionality of a polymer brush layer formed upon adsorption of polymeric micelles on hydrophilic and hydrophobic surfaces. The micelles consist of oppositely charged polyelectrolyte blocks (poly(acrylic acid) and poly(N-methyl 2-vinyl pyridinium iodide), and a neutral block (poly(vinyl alcohol)) or neutral grafts (poly(ethylene oxide)). The strength of the attachment of the micellar layers to various substrates was evaluated with Atomic Force Microscopy. Flow cell experiments allowed for the evaluation of long-term stability of coatings in lateral flow. Fixed angle optical reflectometry was used to quantify protein (BSA) adsorption on the micellar layers after their exposure to flow. The results show that adsorbed micellar layers are relatively weakly attached to hydrophobic surfaces and much stronger to hydrophilic surfaces, which has a significant impact on their stability. Adsorbed layers maintain their ability to suppress protein adsorption on hydrophilic surfaces but not on hydrophobic surfaces. Due to the relatively weak attachment to hydrophobic surfaces the structure of adsorbed layers may easily be disrupted by lateral forces, such that the complex coacervate-brush structure no longer exists.

Modification of Surface Wettability through Adsorption of Partly Fluorinated Statistical and Block Polyelectrolytes from Aqueous Medium

The wetting properties of electrostatically charged hydrophilic substrates were modified through adsorption of ultrathin layer of amphiphilic block or statistical polyelectrolyte from aqueous medium. The studied polymers were copolymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2,2,2-trifluoroethyl methacrylate (TFEMA). They were adsorbed on mica from varying pH conditions, either as dissolved unimers or as kinetically trapped aqueous nanoparticles. The structures (by atomic force microscopy) and wetting properties (by dynamic contact angle measurements) of the obtained surface layers were determined. The majority of the surface layers consisted of polymeric nanoparticles with varying surface coverage. Annealing at 150 °C flattened and spread the particles on the surfaces. The surface wettability was found to be significantly influenced by the morphology and chemical composition of the obtained polymeric surface layer. The surfaces with the most homogeneous and smooth polymer layers exhibited the lowest contact angle hysteresis. The advancing/receding contact angles on the most hydrophilic copolymer layer on mica were 47°/<20°, and on the least hydrophilic layer they were 96°/63°. On unmodified mica surface the water contact angle is ∼0°. When those copolymers that provided the highest contact angles on mica were adsorbed on cellulose fiber substrates and annealed at 120 °C, highly hydrophobic surfaces were obtained, with advancing contact angles around 160°.